A detonator fuze is known having a rotor which is aligned centrifugally when the shell is spun at high speeds. A contact or primer pin is engageable against this rotor axially by spring pressure when it has been released by a ball-type detent which is normally held shut by a spring wound about an axis parallel to the direction of displacement. When the shell is fired the rifling of the gun barrel imparts considerable spin to the shell so that the spring pulls away from the ball-type detent, allowing the pin to move into alignment with the centrifugally oriented rotor and arm the projectile. Before the projectile is spun in this manner it is bore safe, that is even accidental dropping or shaking up of the projectile cannot explode it.
This bore safety of the detonator must exist not only prior to firing the projectile, but also for a brief time after it is fired, as the projectile must not explode as soon as it leaves the muzzle of the gun or even be able to explode immediately as it leaves the muzzle. To this end a relatively long spring is wound around the ball-type detent so that a certain period of time is necessary in order for the entire length of spring to unwind and allow the pin to move into the armed position. As a result of this multiturn construction there is considerable friction force so that it is almost impossible to calculate just when the projectile will be armed after it is fired. Furthermore the balls of the detent are themselves urged centrifugally outwardly with considerable force, and frequently press on and deform the inner turns of the spring. This deformation again increases the arming time so that it is not rare in such arrangements that a projectile strikes a given target before it is armed.
It has been suggested to avoid this latter inconvenience, deformation of the inner turns of the spring, by providing a relatively hard split sleeve or the like within the spring, so that a relatively soft spring, for instance made of synthetic-resin material, may be employed. Such an arrangement increases the construction cost of the fuze and adds to its size and bulkiness. Since the fuze must be fitted within a given projectile which is intended to explode and destroy itself, it is essential that the size of the fuze be reduced to a minimum in order to maximize the amount of powder that can be accommodated in the bursting explosive.